The 4xx directional class is used in case of user committed error, like syntax error, or when a request cannot be fulfilled. HTTP 400 directional code indicates that an error was committed by the user. This error can be a syntax error or due to mistyping. Server is not able to understand the requested URI. The user can make necessary adjustment if he thinks there is any. The error will, most probably, be removed and the requested page will be displayed. HTTP 400 is also known as ‘bad request’.